1. Field of Invention
The present invention relates to a circuit and a tracking method, and in particular, to a control circuit and a tracking method of a maximum power.
2. Related Art
In the recent years, in the wake of heightened environmental consciousness and petrochemical energy such as petroleum and coal is running out, countries worldwide have started to realize an importance of developing new energy. Because sunlight is an energy, which is inexhaustible in supply and always available for use, we do not have to worry that it will run out and the problem with monopolization can also be avoided. Therefore, countries worldwide are devoted to developing applied technology of solar energy, expecting to be less dependable on petrochemical energy by increasing the utilization of solar energy. Solar energy is mainly applied to solar cell or also called photovoltaic (PV) cell, by which light energy is directly converted into electric energy, and an output power can be supplied for a load device.
Referring to FIG. 1A, it shows characteristic curves of an output voltage (VPV) and an output current (IPV) of a conventional solar cell under four different sunlight intensities. It is shown in the figure that under different sunlight intensities, the characteristic curves of the voltage and the current only change on different levels, but curvatures of the characteristic curves remain the same.
In addition, the characteristic curves are divided into a current source region A, a voltage source region B and a maximum power region C (the characteristic curve of a sunlight intensity of 1000 W/m2 is used as an example) based on output characteristics of the solar cell. When a power required by a load is smaller than a maximum power supplied by the solar cell (i.e. the load current is smaller, and an output power of the solar cell is adequate for the load), an operating point for the solar cell is located in the voltage source region B. Besides, when the power required by the load is larger than the maximum power supplied by the solar cell (i.e. the load current is larger, and the output power of the solar cell is not adequate for the load), the operating point for the solar cell is located in the current source region A. Furthermore, when the power required by the load is equal to the maximum power supplied by the solar cell, the operating point for the solar cell is located in the maximum power region C, and the solar cell has the maximum power output.
FIG. 1B is a block diagram of a conventional photovoltaic control circuit 1 with a maximum power tracking function. Referring to FIG. 1B, the photovoltaic control circuit 1 controls and converts an output of a solar cell module PVM for supplying a load device L. The photovoltaic control circuit 1 comprises a conversion unit 11, two analog and digital converters 12 and 13, a gate driving unit 14, and a control unit 15.
The conversion unit 11 is electrically connected to the solar cell module PVM and the load device L, and converts an output signal P1 of the solar cell module PVM into a driving signal P2 for the load device L. Furthermore, the analog and digital converters 12 and 13 are respectively electrically connected to the solar cell module PVM, the conversion unit 11 and the control unit 15, and respectively converts an analog output signal P1 outputted by the solar cell module PVM and an analog driving signal P2 outputted by the conversion unit 11 into digital signals, for inputting into the control unit 15, respectively. The control unit 15 is electrically connected to the gate driving unit 14, and receives outputs from the analog and digital converters 12 and 13 to generate a control signal P3 to control an actuation of the gate driving unit 14, and thus to control an actuation of the conversion unit 11. Accordingly, an output power of the solar cell module PVM is controlled within the maximum power region C as shown in FIG. 1A, and the solar cell module PVM has a maximum power output for the load device L.
However, the control unit 15 of the photovoltaic control circuit 1 typically employs a digital chip, such as a field-programmable gate array (FPGA) processor, a digit signal processor (DSP) or a programmable interface controller (PIC). Moreover, because the digital chip is used, the photovoltaic control circuit 1 requires two analog and digital converters 12 and 13 for signal conversion. Thus the circuit cost for the photovoltaic control circuit 1 will be fairly high.
Therefore, it is an important subject of the present invention to provide a control circuit and a tracking method of a maximum power for limiting an output power of a power output module within a maximum power region, with a lower circuit cost.